Japanese Patent Application Publication No. 2001-166556 discloses an image forming apparatus including a housing, a photosensitive drum, an LED array, a developing unit, a belt, and a transfer roller. The LED array exposes the photosensitive drum to light, so that an electrostatic latent image is formed on a peripheral surface of the photosensitive drum. The developing unit supplies toner to the photosensitive drum, so that the electrostatic latent image is developed to form a toner image on the peripheral surface of the photosensitive drum. The belt is positioned below the photosensitive drum. The belt runs in a horizontal direction while contacting the photosensitive drum. The toner image is transferred onto the belt, and then further transferred from the belt to a sheet by the transfer roller.
The developing unit is attachable to and detachable from the housing of the image forming apparatus. The developing unit and the LED array are arrayed in a running direction of the belt in a state where the developing unit is attached to the housing of the image forming apparatus.